1. Field of the Invention
This invention relates to a magnetoresistance effect film useful in a magnetoresistance effect device employed, for example, to read as signal information or the like recorded on a magnetic recording medium or the like, and more specifically to a magnetoresistance effect film which shows a large rate of change in resistance in a small external magnetic fields.
2. Description of the Related Art
In recent years, high sensitization of magnetic sensors and high densification in magnetic recording are under way. Keeping step with this, active developments have been conducted with respect to magnetoresistance effect magnetic sensors (hereinafter called "MR sensors") and magnetoresistance effect magnetic heads (hereinafter called "MR heads"). MR sensors and MR heads each detect a change in resistance at a read sensor made of a magnetic material to read an external magnetic field signal. In these MR sensors and MR heads, their reproduction outputs do not depend on their relative speeds with recording media, leading to the merit that the MR sensors have high sensitivity and the MR heads provides high outputs in high-density magnetic recording.
Proposed recently is a magnetoresistance effect film having at least two ferromagnetic thin films stacked one over the other with a non-magnetic thin film interposed therebetween and an antiferromagnetic thin film arranged adjacent to one of the ferromagnetic thin films so that said one ferromagnetic thin film is provided with antimagnetic force. When an external magnetic field is applied to this magnetoresistance effect thin film, the one ferromagnetic thin film and the other ferromagnetic thin film are magnetized in different directions under the external magnetic field, whereby a change takes place in resistance (Phys. Rev. B, 43, 1297, 1991; Japanese Patent Laid-Open No. 358310/1992).
Although the magnetoresistance effect device of the preceding application is operable in small external magnetic fields, each signal magnetic field must be applied in the direction of an easy magnetization axis when it is used as a practical sensor or magnetic head. It is therefore accompanied by the problems that, when employed as a sensor, no change in resistance is exhibited around the zero magnetic field and non-linearity such as when a Barkhausen jump appears.
Further, there is a ferromagnetic interaction between the ferromagnetic thin films which are located adjacent to each other with the non-magnetic thin film interposed therebetween, resulting in the problem that a linear range in an MR curve is shifted from the zero magnetic field.
Moreover, it is necessary to use FeMn, a material having poor corrosion resistance, as the antiferromagnetic thin film. This involves the problem that upon practice, an additional measure is needed such as incorporation of an additive or application of a protective film.
When an oxide antiferromagnetic material excellent in corrosion resistance is formed into a film at a room temperature to provide the antiferromagnetic thin film, on the other hand, the biasing magnetic field is small so that the coercive force of the adjacent ferromagnetic thin film becomes large. This has led to the problem that a magnetization anti-parallel state can hardly be obtained between the ferromagnetic thin films.
Because of the construction that a change in resistance is obtained basically by using a change in the length of mean free path of conduction electrons across the three layers of the magnetic/non-magnetic/magnetic films, the above-described conventional magnetoresistance effect films are accompanied by the problem that they show smaller rates of change in resistance compared with magnetoresistance effect films having multilayer structures and called the "coupling type".